In the hot summer, it is absolutely very pleasant to have a cold drink or a plate of cold fruit. For modern people, making ice cubes is very simple. Just have a refrigerator, so both adults and children can easily make ice.
But for the ancients who didn’t have a refrigerator, how should they make ice cubes?
2000 years ago in the Han Dynasty, there was a book called " Huainan Wanbishu ". This book was written in the 2nd century BC. The author was Western Han Dynasty Huainan King Liu An and his disciples. In the book, he recorded a method called "Summer ice making".
The original text is: "Pick the boiling soup and put it in a jar, and use a new pot (jiān) to make ice in three days."
What does it mean?
means boiling the water and pouring it into the "Wen", then sealing it with a clean "sweet" (a kind of silk fabric), then slowly sink the "Wen" into a deep well, and you can get a large amount of ice after waiting for three days. Is
very magical?
We have seen water wells. Can ice be obtained by sealing the boiling water and sinking it into the well? Let’s talk about this question that has puzzled countless physicists.
Pressure Conjecture
In the view of some physicists, the "summer ice-making method" invented by more than 2,000 years ago by , the "summer ice-making method" invented by people in the Han Dynasty actually uses the pressure principle. Sealing the container filled with boiling water and sinking it to the bottom of the well can cause a huge temperature difference on the surface of the container. As the water temperature in the container drops rapidly, the air pressure in the container also decreases, and the water may become ice.
may not be able to understand this phenomenon, so let’s talk about it in detail.
Even in summer, the temperature of the well water is very cool, especially in some deep wells, whose temperature can even reach 3-4℃ in summer. But if you want the water to freeze, you must make the temperature reach 0 degrees, otherwise the water will not turn into ice. This is the knowledge in junior high school physics textbooks, everyone knows.
But there is another "special case" here - the freezing temperature of water, that is, the freezing point of , can change.
For example, if we climb to the top of the world, the Himalayas and boil water here, as long as the temperature is burned to 73.5 degrees Celsius, the water will boil.
For example, the pressure cooker we use at home has a sealed lid that causes the steam in the pot to be unable to be discharged, so the air pressure in the pressure cooker will continue to increase, which also leads to an increase in the boiling point temperature of the water.
Under normal circumstances, the air pressure in the pressure cooker can reach 1.3 atmospheres and the temperature can also reach 125℃.
The boiling point of water will vary according to the air pressure, and the freezing point is the same.
The lower the air pressure, the icing temperature of the water will increase accordingly. According to the test, for every atmospheric pressure reduction, the icing temperature will increase by 0.008℃.
Pressure can increase the freezing temperature of water. Can it be cracked by the "summer ice-making method"?
The answer is impossible!
According to the technological level of in the Han Dynasty , even if the air pressure in the container is reduced to a minimum, the freezing temperature of water can only increase by 1℃.
That is to say, even if we place the container in a deep well with a temperature of only 3℃ and then minimize the air pressure in the bottle, it still cannot meet the icing requirements. Since
is not a pressure principle, what is the reason?
air conditioner cooling guess
It is estimated that many friends have let the tires of the bicycle be aired. When we unplug the valve core , the gas in the tire will gush out in a very short time, and the tire valve will become particularly cool.
This phenomenon occurs because the pressure change leads to a sudden change in temperature, which is also one of the principles that air conditioners can refrigerate.
So did the "summer ice-making method" in the Han Dynasty use this principle?
To prove this conjecture, physicist Professor Li Zhichao guided graduate student Zhao Hongjun to conduct a simulated ice-making experiment.In order to achieve the best experimental results, they found a glass ball bottle with a large body and a small mouth instead of the urn.
containers like this were absolutely impossible to make in the Han Dynasty, but if you want to maximize the effect of "pressure mutation", you must use containers of this shape.
The bottle mouth of the glass bottle is sealed with a rubber stopper. There is an glass tube with a thermometer in the stopper, which reaches the bottom of the bottle. On the outside of the plug is a hose, and there is also a clamp that can adjust the elasticity on the hose.
When you are ready, fill the glass ball bottle with water, then heat it so that the water will boil completely, leaving only the amount of water that is not across the glass tube mouth, then clamp the hose with a clip and quickly put the glass ball bottle into the bucket filled with cool water.
If you want to experiment, you must pay attention. There are dangers here!
The temperature of the glass bottle is very high, and it is very likely to explode when it is quickly immersed in cool water with very low temperatures. For example, when we drink wine in winter, in order to warm the wine, we will put it in boiling water and burn it, but if we don’t pay attention, we will burn the bottle.
When the glass ball bottle is immersed in cool water, the water temperature drops very quickly, from 100℃ to around 20℃, but then the water temperature drops begin to become very slow.
20℃ is still a lot larger than 0℃ when water can freeze. Is it because the placement time is relatively short? After all, the "Summer Icemaking Method" said that it takes three days to get ice, so Professor Li Zhichao placed the glass ball bottle for a few more hours.
Finally, the water temperature in the glass ball bottle was maintained at around 7℃. At this time, slowly loosen the clamp, and the water temperature in the glass bottle dropped by about 1℃.
Since then, the test has ended, and the results show that the water temperature can only drop to around 6℃ and cannot meet the freezing conditions.
Although the experiment did not achieve the effect, Li Zhichao believed that his guess was correct. He put the heated water in cold water to cool it, and then opened the sealed container for ventilation. As long as the conditions can be met, it is entirely possible to create ice cubes, but the premise is that a very special fine-mouthed and big belly bottle is needed.
Later, some physicists used various containers to make ice using the "summer ice-making method". Most of the experiments ended in failure, but some people were very lucky to get some ice slags instead of the ice cubes mentioned in the "summer ice-making method".
Unsolvable doubts
Although physicists have never obtained ice cubes through the "ice-making method", their research direction is not wrong. As for where the problem lies, it is unknown.
After all, the ancients did not record the "summer ice-making method" in detail. No one knows what the container "Wang" looks like. No one knows what "new product" is, and I think there are some key technologies that have not been recorded.
With today's scientific research technology, it is impossible to answer the problem of "summer ice making method". It is estimated that the demand conditions for this ice making technology are very strict. During the Han Dynasty, except for princes and nobles, ordinary people must not be able to use the "summer ice-making method".
Of course, ordinary people also have other ways to get ice, such as building an ice cellar. They only need to remove the ice cubes in winter and store them properly in the ice cellar. In summer, they can use ice cubes.
This situation changed completely when Tang Dynasty . Tang people discovered that
As long as saltpeter is put into water, it can quickly dissolve in water and absorb heat, so the water will turn into ice.
Even in the hot summer, saltpeter can freeze water quickly. This simple ice-making technology quickly spread throughout the country, and the high-end "summer ice-making technology" was completely replaced and disappeared into the long river of history.
